Really? The Last time I was in an American office, there didn't seem to be any milk around. They had an unrefrigerated bottle of "creamer" next to the coffee machine, but I was too scared to try it. I'm still not sure what it is, or how I'm supposed to use it.
Creamer is a liquid made with oil and sweetener that approximates the taste and mouthfeel of milk and sugar. Or really a flavored syrup, not sugar. They often have hazelnut or vanilla flavoring added. You would use it by pouring it in your coffee, at about a 1:1 ratio with how you would use milk.
I'm surprised you associated it with espresso. Creamer and drip coffee machines go together. Milk and espresso machines go together. I've seem drip coffee machines with real milk, but I've never seen an espresso machine with just creamer.
It tends to exist primarily in office environments, because it can stand not to be refrigerated and was the first lactose-free option. Therefore it was easy to buy one bottle and solve the problem of "stuff to add to coffee".
It is not an espresso. The temperature and pressure are lower than an espresso machine. The results would be considered analogous to more American style coffee. Meant to be drunk from a full mug (~177ml to ~298ml), etc.
It's marketed as a coffee machine that makes a single cup with a single pod at a time.
(Apparently you can tweak a Keurig to approach an espresso, but it's not the default).
Office coffee is not what people drink for pleasure -- it's a caffeine delivery device. If you go to a coffeehouse in the US you'll find that people often order drinks called Lattes which is espresso and steamed milk. And the word is Italian like espresso itself, so I think this isn't some weird Americanism but pretty traditional.
Every single coffee shop I’ve ever been in that serves espresso also serves lattes. Philz does not serve espresso, they only serve coffee. You went to virtually the only coffee shop in the US that does not serve lattes.